The purpose of this proposal is to develop a multifunctional nanoparticle platform for epitope presentation on gold nanoclusters with immunological analysis for the creation of nanotechnologies that target the immune system. The future development of nanoparticle-based vaccines requires the generation of protein structures that faithfully recapitulate the conformation of protective antigens of pathogenic microorganisms. Ironically, our ability to logically design recombinant or synthetic protein antigens that are protective is quite limited. As most epitopes on native proteins are likely to be assembled, one of the most significant challenges facing epitope determination efforts is the identification of conformationally assembled epitopes. We hypothesize that the presentation of target protein loop structures on the surface of gold nanoclusters will present a statistically significant diversity of potential loop conformations to provide the foundation of a new method for discovering unknown epitopes of pathogenic toxins. To demonstrate the feasibility of this approach, we are creating an epitope-labeled nanocluster that mimics the protective antigen (PA) of Bacillus anthracis. In this proposal, our goal is to refine and extend our conceptual strategies for epitope presentation on nanoclusters via the following specific aims: 1. Design, synthesize, and assemble linear and conformational epitopes on the surface of gold nanoclusters. 2. Determine which of the conformational peptide loop constructs faithfully represent the naturally occurring immunogenic structures in native protein. 3. Screen mouse and human antibody libraries, and patient sera using epitopes presented on nanoclusters working towardsthe development of a diagnostic microarray. 4. Optimize the immunological response of multifunctional nanoparticles in mice. Specific challenges in nanotechnology will be the creation of specific substructures on a nanoparticle surface, immunorecognition of these specific conformations, creation of multifunctional nanoparticles, and correlation of peptide loop structure as a function of nanoparticle size and curvature. Specific changes in biology and medicine include the discovery of unmapped linear and conformational epitopes, the immune system response to functionalized nanoparticles, the screening of antibodies libraries for conformational epitopes, and ultimate development towards conformational epitope-labeled nanoparticles as potential vaccines.